THE GLOBAL FLUX OF P IN FERTILIZERS, CROPS, AND LIVESTOCK PRODUCTS RESULTS IN MANY SOILS WITH AN EXCESS OR DEFICIENCY OF P. ABOUT 30% OF GLOBAL CROPLANDS ARE P-DEFICIENT, MOST OF WHICH ARE IN DEVELOPING COUNTRIES THAT CANNOT AFFORD P FERTILIZATION AND THUS SUFFER FROM REDUCED CROP YIELDS (CORDELL, DRANGERT AND WHITE, 2009; MACDONALD ET AL., 2011). ON THE OTHER END OF THE SPECTRUM OF SOIL P LEVELS, "HOT SPOTS" LIKE THOSE IN CHINA AND THE U.S. RECEIVE 50% OF THE GLOBAL FERTILIZER APPLICATION AND YET REPRESENT ONLY 10% OF FERTILIZED LAND (POTTER ET AL., 2010). DOWNSTREAM TRANSPORT OF P FROM CROP LANDS ADDS TO THE ACCELERATING EUTROPHICATION OF SURFACE WATER (BENNETT, CARPENTER AND CARACO, 2001; SHARPLEY, 2016). AS SEEN IN THE CHESAPEAKE BAY, P-LOADING INCURS SIGNIFICANT ENVIRONMENTAL AND ECONOMIC COSTS (ATOR, BRAKEBILL AND BLOMQUIST, 2011). THE ECONOMIC AND ENVIRONMENTAL CONSEQUENCES OF SOIL P LEVELS OUTSIDE OF AN OPTIMUM RANGE REQUIRES RESEARCH INTO THE SOIL CONDITIONS THAT MOVE THE SOIL FROM A P SOURCE FOR PLANT GROWTH TO A P SOURCE FOR WATER POLLUTION.THIS PROPOSAL TAKES AN EXPERIMENTAL AND A MODELING APPROACH TO UNDERSTANDING THE MECHANISMS UNDERLYING THE MOVEMENT AND AVAILABILITY OF P IN THE SOIL. FOR THE EXPERIMENT, INNOVATIVE P TRACING METHODS WILL BE USED TO FOLLOW THE TRANSFER OF P BETWEEN SPECIFIC SOIL COMPARTMENTS THAT RANGE IN THEIR CAPACITY TO STABILIZE P. THIS WILL PROVIDE IMPORTANT SOIL-SCALE INSIGHTS INTO HOW P BECOMES STABILIZED (LIMITING PLANT AVAILABILITY) OR DESTABILIZED (INCREASING RISK FOR RUNOFF AND LEACHING) IN THE SOIL. THE MODELING PORTION INVOLVES INTEGRATING THE TRACER EXPERIMENT RESULTS INTO A P CYCLING MODEL. THE P CYCLING MODEL WILL THEN BE INTEGRATED INTO THE GREATER FRAMEWORK OF THE SIMULATION MODEL CYCLES WHICH CAN BE USED TO MODEL CURRENT AND FUTURE CHANGES IN CROP GROWTH AND SOIL NUTRIENT DYNAMICS. IT IS CURRENTLY BEING USED BY A RANGE OF RESEARCHERS, EXTENSION WORKERS, AND STUDENTS AND HAS RECENTLY BEEN DEVELOPED INTO AN ONLINE VERSION ACCESSIBLE TO A WIDER USER-BASE, INCLUDING FARMERS. THE ULTIMATE GOAL OF THE EXPERIMENT AND MODEL DEVELOPMENT IS TO UNCOVER SOME OF THE BIOGEOCHEMICAL PROCESSES THAT CONTROL THE AVAILABILITY OF P IN AGRICULTURAL AND NATURAL ECOSYSTEMS. THIS KNOWLEDGE WILL NOT ONLY HELP CREATE MODELS THAT WE RELY ON TO ASSESS AGRICULTURE IN A CHANGING WORLD, BUT WILL PROVIDE IMPORTANT INSIGHTS INTO HOW CURRENT MANAGEMENT PRACTICES AFFECT THE CONTROLS ON THE MOVEMENT AND AVAILABILITY OF P.REFERENCESATOR, S. W., BRAKEBILL, J. W., & BLOMQUIST, J. D. (2011). SOURCES, FATE, AND TRANSPORT OF NITROGEN AND PHOSPHORUS IN THE CHESAPEAKE BAY WATERSHED: AN EMPIRICAL MODEL. US GEOLOGICAL SUREY, 5167.BENNETT, E. M., CARPENTER, S. R., & CARACO, N. F. (2001). HUMAN IMPACT ON ERODABLE PHOSPHORUS AND EUTROPHICATION: A GLOBAL PERSPECTIVE. BIOSCIENCE, 51(3), 227-234.CORDELL, D., DRANGERT, J. O., & WHITE, S. (2009). THE STORY OF PHOSPHORUS: GLOBAL FOOD SECURITY AND FOOD FOR THOUGHT. GLOBAL ENVIRONMENTAL CHANGE, 19(2), 292-305.MACDONALD, G. K., BENNETT, E. M., POTTER, P. A., & RAMANKUTTY, N. (2011). AGRONOMIC PHOSPHORUS IMBALANCES ACROSS THE WORLD'S CROPLANDS. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES, 108(7), 3086-3091.POTTER, P., RAMANKUTTY, N., BENNETT, E. M., & DONNER, S. D. (2010). CHARACTERIZING THE SPATIAL PATTERNS OF GLOBAL FERTILIZER APPLICATION AND MANURE PRODUCTION. EARTH INTERACTIONS, 14(2), 1-22.SHARPLEY, A. (2016). MANAGING AGRICULTURAL PHOSPHORUS TO MINIMIZE WATER QUALITY IMPACTS. SCIENTIA AGRICOLA, 73(1), 1-8.

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